1. Field of the Invention
This invention relates to a method for manufacturing a reformed titanium trichloride which, in the polymerization of .alpha.-olefin, makes it possible to obtain a highly stereospecific polymer with a high polymerization activity.
2. Discription of the Prior Art
Either in the presence or in the absence of an inert solvent, a catalyst system comprising a halide of a metal selected from the groups IV, V and VI of the periodic table and an organometal compound of a metal selected from the groups I, II and III of the periodic table has generally been known as Ziegler-Natta catalyst.
For example, titanium trichloride, which is selected from halides of the metals belonging to the groups IV, V and VI of the periodic table, and an organoaluminum compound which is selected from organometal compounds of the metals belonging to the groups I, II and III, are in use as catalyst for the polymerization of .alpha.-olefin such as propylene and have brought about good results.
The titanium trichloride manufacturing method is well known. Namely, a solid solution or a crystalline compound comprising aluminum trichloride and titanium trichloride which is obtained from the reduction of titanium tetrachloride with metal aluminum in the presence of aluminum trichloride and which is approximately of a structure of 3TiCl.sub.3.AlCl.sub.3 is pulverized by means of various pulverizers. The titanium trichloride which is prepared through such processes is being advantageously used for industrial purposes.
When .alpha.-olefin is polymerized using the above mentioned catalyst system, it is extremely advantageous for industrial purposes to enhance the formation ratio of stereospecific polymer, that is, the isotactic yield (hereinafter called "I.Y.") and the catalyst efficiency of titanium trichloride, that is, the polymerization activity.
On the one hand, for a higher catalyst efficiency, therefore, there have been attempted various methods such as broadening the specific surface area of titanium trichloride by pulverizing it into finer particles.
Such a simple method of physical pulverization into finer particles alone not only does not bring about any great improvement in the polymerization activity of titanium trichloride but also produces a degraded particle characteristic of the polymer product because of the formation of fine polymer particles to a great extent when such a finely pulverized titanium trichloride is employed as a component of a catalyst in the polymerization of .alpha.-olefin.
A catalyst system comprising titanium trichloride and triethylaluminum brings about higher polymerization activity but results in the formation of a considerable amount of an amorphous polymer generally termed atactic polymer which is of a low economic value, so such a catalyst system is disadvantageous for industrial use because of complicating processes after polymerization.
On the other hand, for higher yield of stereospecific polymer, there have been proposed various methods such as adding what is called a third component into polymerization system and using titanium trichloride mixed with a third component in a pulverizer as a component of a catalyst system. According to these methods, the initial purpose to improve I.Y. can be successful, but the added third components often cause adverse effects on the polymerization activity. Moreover, when they are contained in polymerization solvents, it generally needs to provide equipments in order to separate them from the polymerization solvents.
When they are contained in polymer products, they also cause coloring and smelling of the polymer products. Therefore any of the methods proposed until now does not always provide satisfactory results on the polymerization of .alpha.-olefin such as propylene.